The invention concerns an AC-powered power supply with an output to feed a load L with a time-variable output DC current I.sub.o via an output line at electric potential V.sub.o and a return line at electric potential zero, with a bipolar controller V controlling the instantaneous value of an output quantity measured with a sensor F.sub.1 in less than a second within a tolerance of 0.1% to a predetermined setting, and with an adjustable rectifier EQ followed by a charging inductance L.sub.1 and a filter capacitor C.sub.1, whereby the output of controller V is electrically connected to the output line of the power supply.
Such a power supply is for example known from the article "New Principle for Power Supplies for Synchrotron Magnets without Tracking Errors" by R. Wagnitz et al. in Proceedings of the 2nd European Particle Accelerator Conference EPAC 90, Nice, 12-16 Jun. 1990, Volume 2, pages 1188-1190.
Controlled power supplies are usually used to supply sensitive electric loads of most different kinds with an amount of electric energy which is as constant as possible and which is as optimally as possible adapted under changing conditions. For example, pulse-width-regulated switch controllers are known in the art, transforming, after power rectification, the generated DC voltage into controllable pulse-width variable current pulses, which, either directly or after high-frequency transformation, are again transformed to DC voltage. A disadvantage of such arrangements is the high frequency interference spectrum which in particular for higher powers is radiated directly out of the circuit leads, when the systems cannot be manufactured in a very compact way. Choice of a lower switching frequency with less interference increases the mechanical dimensions. For highly precise control circuits, the limitation of the control bandwidth which is given by the switching freqency (20 kHz to 500 kHz), is a substantial disadvantage. The efficiency of switching processes is higher than that of analog control circuits.
A different type of controlled power supplies are the so-called linear controllers or analog controllers. Hereby, the control transistors are not switched and their complete family of operating curves may be used. An advantage of these systems is their nearly ideal frequency response, which guarantees little phase shift up to the MHz range. In addition, if correctly dimensioned, there are always sufficient reserves even for large control amplitudes if large amplitude oscillations occur. However, a disadvantage of linear controllers is that, because of the use of the transistors as controlled resistors, a permanent Ohmic loss (10% -100%) has to be accepted, resulting in a rather low efficiency of such power supplies.
The efficiency of a linear controller can be improved if a pre-control element is employed. In this case, the complete theoretically possible family of operating curves between zero and full power is not used, rather the control is limited to the amplitude range of the actually occurring interferences in the control circuit. The linear controller on its own produces no high frequency interferences and is therefore particularly suitable if interference-sensitive apparatuses are used in its surroundings. However, the still high power losses remain a disadvantage, which in practice can hardly be reduced below 10%, since also for the linear controller with pre-controlling, the full output current is directed across the servo element.
In contrast, a considerably higher efficiency is obtained with an active filter for AC voltage. Such active filters are for example known from the article "Very High Precision Current Power Supplies for the FERMILAB ANTIPROTON SOURCE" by McCarthy et al., published in the "Particle Accelerator Conference at Vancouver, Canada", May 1985. In an active filter, a pre-controller with low bandwidth is used, which can be derived from the mains frequency or a multiple thereof. In addition, there is at least one additional controller which can be used in higher frequency ranges than that of the pre-controller. The control-variable of the control circuit is thereafter analysed and, depending on the actual value, control deviations in different frequency ranges are supplied to the different controllers. Interferences at higher frequencies can be compensated by active elements. By distributing the correction to different control channels, a comparatively high control bandwidth as well as a high amplification at relatively low power losses can be obtained, but such a power supply very soon becomes relatively complex for high power rates. All control channels following the pre-controller do not allow DC control since they are not electrically coupled. Use of a combination of different controllers with different phase and frequency responses makes it difficult to assemble a total family of operational curves for the power supply from the individual control steps which is suitable for stable control. Under certain operating conditions, oscillations are possible.
In a power supply according to the document cited at the beginning, a higher stability is reached by combining the active filter with a linear controller. However, the frequency response problems as well as the extremely high complexity of the arrangement for high control and amplification requirements also remain in this optimized prior art system. In addition, this system still needs a quadrature current of more than 3%, resulting in an average efficiency of at best 97%.
It is therefore the purpose of the present invention to introduce an AC driven power supply of the above mentioned kind which on the one hand is not limited in its bandwidth by the controller and which therefore operates extremely stably, and which on the other hand has a control efficiency of 99% or better and which can, finally, be realised by a very simple construction even for high output power and precision requirements.